AbstractGut microbiota is essential to human health, playing a major and important role in the bidirectional communication between the gut and the brain. There is significant evidence linking gut microbiota and metabolic disorders such as obesity, diabetes and neuropsychiatric disorders such as schizophrenia, autism, anxiety, depression. New studies show microbiota can activate immune system, neural pathways and central nervous system signaling systems, including commensal, probiotic and pathogenic microorganisms in the gastrointestinal tract. This microorganisms are capable of producing and delivering neuroactive substances such as gamma-aminobutyric acid and serotonin, which act on the gut-brain axis. Preclinical evaluation in rodents suggests that certain probiotics possess antidepressant or anxiolytic activity. Effects may be mediated via the vagus nerve, spinal cord, immune system or neuroendocrine systems. Here we review recent literature that examines the impact of gut microbiota on the brain, behavior and psychiatric disorders.